A while ago I made a set of bookshelves and added slots to the shelves. It took me a lot of time and effort, but finally I worked out how to do it. So I made a tutorial. This is in no way meant to replace the excellent tutorials already on site, its just a different perspective on the same topic. This can be handy for creators - having more than one person explain the same thing can help to understand.

My tutorial does not tell you much about the whys and wherefores - it's just a step by step list to making slots. If you want more background I suggest you check out Huge Lunatics excellent tutorial.